Naming compounds Roman numerals

MgCls Magnesium is a metal that always forms a +2 ion. This ionic compound is named without Roman numerals or prefixes magnesium chloride. 

Nitrogen trichloride. Although this is a binary compound of two nonmetals, it can be named with Roman numeral designations. It is indeed possible to call this nitrogen(III) chloride in the most modern usage, but most chemists do not do that yet. 

Select all of the following compounds that should be named using the prefixes of Table 6.1, all that should be named with Roman numerals, and all that should have neither. Name each. 

Names of ionic compounds are derived from the names of their ions. The name of the cation appears first, followed by the name of the anion. In the Stock system for naming an ion (the systematic name), a Roman numeral indicates the charge of the cation. In the older common nomenclature system, the suffix -ous indicates the lower of the ionic charges, and the suffix -ic indicates the higher ionic charge. 

In naming the compounds of transition or post-transition metals, we ordinarily indicate the charge of the metal cation by a Roman numeral ... 

The name of a monatomic cation is the same as the name of the element forming it, with the addition of the word ion, as in sodium ion for Na+. When an element can form more than one kind of cation, such as Cu+ and Cu2+ from copper, we use the oxidation number, the charge of the cation, written as a Roman numeral in parentheses following the name of the element. Thus, Cu+ is a copper(I) ion and Cu2+ is a copper(II) ion. Similarly, Fe2+ is an iron(II) ion and Fe3" is an iron(III) ion. As shown in Fig. C.6, most transition metals form more than one kind of ion so unless we are given other information we need to include the oxidation number in the names of their compounds. 

Oxidation state is a frequently used (and indeed misused) concept which apportions charges and electrons within complex molecules and ions. We stress that oxidation state is a formal concept, rather than an accurate statement of the charge distributions within compounds. The oxidation state of a metal is defined as the formal charge which would be placed upon that metal in a purely ionic description. For example, the metals in the gas phase ions Mn + and Cu are assigned oxidation states of +3 and +1 respectively. These are usually denoted by placing the formal oxidation state in Roman numerals in parentheses after the element name the ions Mn- " and Cu+ are examples of manganese(iii) and copper(i). 

Name compounds by applying the guidelines. The guidelines for naming binary compounds that contain metals differ from those for compounds containing no metal. Unless a metal forms only one stable atomic cation, its charge must be specified with a Roman numeral in parentheses. 

Cr03 As a transition metal, chromium forms more than one stable cation. Name the metal first, using a Roman numeral to designate chromium s charge. Each of the three oxide anions has a -2 charge. To maintain net charge neutrality, Cr must be +6, so the name of the compound is chromium(VI) oxide. 

Some metals, such as iron, can form more than one type of ion. Iron ions can either have a +2 or a +3 charge. Chemists use Roman numerals to distinguish between the two different types of iron ions. The Roman numeral II in the name of the chemical compound iron(II) sulfide means that the iron ion in this compound has a +2 charge. 

Different modifications of a compound are frequently designated by lower case Greek letters a, j3,..., e.g. a-sulfur, j3-sulfur, or by roman numerals, e.g. tin-I, tin-II etc. Polymorphic forms of minerals have in many cases been given trivial names, like a-quartz, P-quartz, tridymite, cristobalite, coesite, keatite, and stishovite for Si02 forms. 

Naming of the positive ion depends on whether the cation is monatomic (has one atom). If not, the special names given in Sec. 6.3.2 are used. If the cation is monatomic, the name depends on whether the element forms more than one positive ion in its compounds. For example, sodium forms only one positive ion in all its compounds—NaT Iron forms two positive ions—Fc2r and Fe,+. Cations of elements that form only one type of ion in all their compounds need not be further identified in the name. Thus, Na may simply be called the sodium ion. Cations of metals that occur with two or more different charges must be further identified. Fe(NO,)2 and Fe(NO,)3 occur with Fc2+ and Fe3 ions, respectively. If we just call the ion the iron ion, we will not know which one it is. Therefore, for monatomic cations, we use a Roman numeral in parentheses attached to the name to tell the charge on such ion. (Actually, oxidation numbers are used for this purpose, but if you have... 

Am. In each ease, the answer is BuS. Part (ft) gives the ions and their charges, and so is perhaps easiest to answer. Part (know that periodic group IIA elements always form 2-t- ions in all their compounds and that sulfur forms a 2- ion in its compounds with metals. It is also necessary to remember that the metal is named first. In part (< ). the fact that there is only one compound of these two elements is deduced by the fact that the barium is stated with no Roman numeral, and that sulfide is a specific ion with a specific (2-) charge. 

For compounds or ions containing elements that have a variable oxidation number, Roman numerals are used to indicate the oxidation number of the element concerned, and so name the chemical species. This is called Stock notation, after the chemist A. Stock who devised the method. 

Name the following compounds using Roman numerals to indicate the oxidation number of the metal ... 

A The name of each of these ionic compounds is the name of the cation followed by that of the anion. Each anion name is a modified (with the ending ide ) version of the name of the element. Each cation name is the name of the metal, with the oxidation state appended in Roman numerals in parentheses if there is more than one type of cation for that metal. 

To avoid the necessity of memorizing a separate name for each ion, we can use the Stock system. In the Stock system, the charge of the cation appears as a Roman numeral immediately after the name of the element. Using the Stock system, we write Fe2+ as the iron(II) ion, and Cu+ as the copper(I) ion. Other than the necessity of indicating the charges, there are no differences between the naming of transition metal compounds and other compounds of the metals. So while KC1 is potassium chloride, CuCl is copper(I) chloride. 

Many transition metals and the group of six elements centered around lead on the periodic table commonly have more than one valence. The valence of these metals in a compound must be known before the compound can be named. Modern nomenclature rules indicate the valence of one of these metals with a Roman numeral suffix (Stock notation). Older nomenclature rules used different suffixes to indicate the charge. Examples ... 

Name the following compounds that contain elements with variable charge. Don t forget to use Roman numerals ... 

Metal cations team up with nonmetal anions to form ionic compounds. What s more, the ratio of cations to anions within each formula unit depends on the charge assumed by the fickle transition metal. The formula unit as a whole must be electrically neutral. The rules you follow to name an ionic compound must accommodate the whims of transition metals. The system of Roman numerals or suffixes applies in such situations ... 

FeCl2 or FeCl3 compound. Therefore iron must include a Roman numeral to specify which cation is in the compound. Iron (II) chloride is FeCl2 and iron (III) chloride is FeCl3. Two or more atoms may combine to form a polyatomic ion. Common polyatomic ions are listed in Table 1.3. The names of polyatomic ions may be used directly in compounds that contain them. Hence, NaOH is sodium hydroxide, CaC03 is calcium carbonate, and Ba(N03)2 is barium nitrate. 

Roman numeral, as though phosphorus were a metal and the oxide present as O2-. Thus, P406 is thought of as (P1+)4(02 )6 and named phos-phorus(III) oxide, and P4O10 is thought of as (P5+)4(O2 )10 and named phosphorus(V) oxide. These compounds, though, are molecular. 

Stock number (1) A Roman numeral equal to the number of electrons lost by an atom on formation of a compound and sometimes added in parentheses to a name. (2) The oxidation number of the element. Example copper(II) in compounds containing Cu2+. stock solution A solution stored in concentrated form. 

For transition metal compounds, the charge on the cation is indicated by the Roman numeral in the name. Knowing the number of positive charges, you can then figure out the number of necessary negative charges for the associated anions. 

Some elements, such as copper and iron, possess two ions with different valencies. Copper can form the Cu+ ion and the Cu2+ ion, with valencies 1 and 2 respectively. Therefore it can form two different compounds with chlorine, CuCl and CuCl2. We can also distinguish the difference by using Roman numerals in their names CuCl is copper(i) chloride and CuCl2 is copper(n) chloride. Similarly, iron forms the Fe2+ and Fe3+ ions and so can also form two different compounds with, for example, chlorine FeCl2 (iron(n) chloride) andFeCl3 (iron(m) chloride). 

The Roman numerals appended to the names of some of the compounds refer to the structural formulas given in the text. 

Many metals may form cations of more than one charge. In this case, a Roman numeral in parenthesis after the name of the element is used to indicate the ion s charge in a particular compound. 

A. Write the name for each of these compounds. Remember that Roman numerals are required. 

The first thing to point out is the charge on tin. While tin has more than one possible charge, you know it has to be two in this case because of the Roman numeral (II) that appears in the name. The formula Sn202 does not represent the smallest ratio of ions. You should notice that if each one of these subscripts is reduced by the new formula will be SnO. You can only reduce these subscripts if all subscripts in a formula can be reduced by the same amount (this will be more critical with ternary ionic compounds). 

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